This proposal requests continued support for a program of research on the perception of speech signals by human adults and infants, particularly the perceptual analysis of syllables, phonemes and distinctive features used in spoken language. The major goal of the proposed work is to seek a better understanding of the acoustic and perceptual basis for phonetic segments and features and how they are analyzed during the earliest stages of speech perception. This work will be carried out with both speech an speech-like signals in order to establish well-defined acoustic attributes for speech. Work will also be directed at several important questions dealing with perceptual development, the role of early environmental experience and the reacquisition and modification of selected phonetic contrasts in mature adults. From this research we hope to learn in what ways speech perception may require specialized perceptual mechanisms and in what ways it may conform to other more general perceptual processes.